1. Field of Invention
The present invention relates to a slurry dilution system with an ultrasonic vibrator capable of in-situ adjustment of the slurry concentration. More particularly, the present invention relates to a slurry dilutions system capable of in-situ adjustment of the concentration of slurry supplied to a chemical-mechanical polishing (CMP) station.
2. Description of Related Art
To match the increasing demand for a higher operating speed of electronic devices, semiconductor manufacturers have developed the deep sub-micron technologies. Due to the reduction of device dimensions, depth of focus in photolithographic equipment decreases while the number of layers of multi-level metal (MLM) interconnects increases. Hence, how to maintain planarity in the manufacturing of silicon chip has become an important issue.
Before the deep sub-micron era of semiconductor manufacturing, spin-on-glass (SOG) used to be the main planarization method. However, the method can only planarize local silicon chip area so that global planarization of the entire wafer chip is still unattainable. Without global planarization, the developed pattern in a photoresist layer is likely to be inferior because of intrinsic limitations of the light exposure station in photolithographic operation. In addition, errors in end-oint detection during etching may occur, resulting in a low yield of silicon chips.
Global planarization of silicon chips is now routinely achieved by chemical-mechanical polishing (CMP). During CMP, slurry is one of the components indispensable for successful polishing. Polishing action is achieved through direct contact of slurry with the surface of a silicon chip. Consequently, slurry supply rate, slurry temperature, pH value of the slurry and the distribution of slurry are all critical factors that affect the quality of a polished surface. In some advanced chemical-polishing machines, the concentration of slurry may have to change according to a predefined pattern, as well.
FIG. 1 is a schematic diagram showing the conventional slurry dilution system of a chemical-mechanical polishing station.
As shown in FIG. 1, raw slurry is passed into a pipeline 102a through a slurry inlet 100a, while de-ionized water for diluting the slurry is passed into a second pipeline 102b through a de-ionized water inlet 100b. The raw slurry in the pipeline 102a and the de-ionized water in the pipeline 102b have to pass through flow meters 104a and 104b, respectively. Hence, the ratio between the incoming raw slurry and the incoming de-ionized water can be monitored and determined according to demand.
Thereafter, the raw slurry and the de-ionized water are passed into a mixer 106 of 10xcx9c100 liters where the two are churned to form diluted slurry having a uniform concentration. The diluted slurry is transferred to a slurry supply tank 108. From the slurry supply tank 108, the diluted slurry can be delivered to a chemical-mechanical polishing station 112 through a supply pipe 110.
However, the average slurry supply tank for storing diluted slurry has a capacity of 100xcx9c10,000 liters in order to keep the concentration of the diluted slurry at a constant. Such a tank occupies a lot of floor space. Moreover, if the concentration of the slurry has to be varied, all of the slurry originally in the supply tank must be removed completely for the new batch of slurry with different concentration. Therefore, it""s not easy to adjust the concentration of the slurry, and too much slurry is wasted during the changeover of the slurry. In addition, a chemical-mechanical polishing operation that demands diluted slurry of different concentrations in sequence must either use a few independent dilution systems, or else the polishing has to be conducted in a number of different chemical-mechanical polishing stations.
The present invention provides a slurry dilution system capable of diluting slurry in-situ to a defined level of concentration. The slurry dilution system occupies very little clean room space but can provide diluted slurry of any concentration to a chemical-mechanical polishing station on demand.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a slurry dilution system. The slurry dilution system includes a first pipeline having a first terminal for the entrance of raw slurry into the system, a second pipeline having a first terminal for the entrance of slurry diluting de-ionized water into the system, a first flow meter installed somewhere along the first pipeline for measuring the rate of flow of raw slurry, a second flow meter installed somewhere along the second pipeline for measuring the flow of de-ionized water, a delivery pipeline having a first terminal connected to the second terminal of both the first pipeline and the second pipeline and the second terminal of the delivery pipeline coupled to a chemical-mechanical polishing station, an ultrasonic vibrator installed near the first terminal of the delivery pipeline for mixing the raw slurry and the de-ionized water and preventing slurry particles from sticking to the pipe walls and forming clumps so that a higher mixing efficiency is obtained, and a mixer installed near the second terminal of the delivery pipeline for preventing the deposition of slurry particles, wherein the delivery pipeline includes at least one turning region between the ultrasonic vibrator and the mixer.
In this invention, raw slurry and de-ionized water fed into the slurry dilution system are mixed and homogenized by the ultrasonic or megasonic vibrator and the small mixer. The well-mixed slurry solution is then delivered to a chemical-mechanical polishing station. When the chemical-mechanical station requires slurry of a different concentration, raw slurry can be diluted to the desired level simply by changing the rate of flow of de-ionized water into the dilution system.
Since there is no need for a special supply tank to accommodate the diluted slurry, the area occupied by the slurry dilution system is smaller. Hence, production cost of the system is also reduced.
The slurry dilution system of this invention can be built inside any chemical-mechanical polishing station. Hence, uniformly slurry diluted to any level can be supplied to the chemical-mechanical polishing station without passing through lengthy pipelines.
By varying the rate of flow of de-ionized water with respect to slurry, the desired degree of dilution can be obtained. Consequently, the dilution system is capable of providing the slurry in any types of chemical-mechanical polishing operations.
The vibration provided by the Ultrasonic vibrator in this invention is capable of increasing the mixing efficiency of the diluted slurry, thereby improving the homogeneity of slurry solution. In addition, if a U-shaped slurry delivery pipeline is used, mixing efficiency can be further increased.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.